Recently, there is an increasing tendency to preserve natural teeth as much as possible and tooth filling treatment is being actively implemented, so more and more attention is paid to filling materials used therefor.
An ideal dental filling composition should be excellent in properties such as biocompatibility, bactericidal property, sealing property, stability, workability, injectability and dispersibility, hardening time, capability for enhancing tooth structure, homogeneity, and radiopacity.
In U.S. Pat. No. 5,415,547 issued in 1995, Prof. Mahmoud Torabinejad at Loma Linda University has disclosed a dental filling composition being hardenable under moist conditions, in which bismuth oxide is added at 20 to Portland cement for radiopacity, and a method for using the same. Thereafter, Dentsply Tulsa Dental, Inc. has released a product under a brand name, ProRoot MTA. As the effectiveness of the product is widely known, there have been developed a variety of similar products such as MTA Angelus (from Angelus), OrthoMTA (from BioMTA), BioAggregate (from Verio Dental), Biodentine (from Septodont) and other bioceramic materials.
The above existing dental filling materials mainly consisting of calcium silicate cement are intended to comprise various heavy metals as much as 10 to 30% to have radiocontrast properties. The heavy metals include bismuth oxide, tantalum oxide, tungsten oxide, barium sulfate and the like, and are not preferable in terms of biocompatibility to be used as dental filling materials prone to directly contacting blood vessels and nerves in a human body.
In connection with addressing the above problem, Korean Laid-open Patent Publication No. 10-2011-0070269 discloses a root canal filling material having good radiopacity and biocompatibility, which comprises zirconia beads at 10 to 100 wt %, preferably at 10 to 40 wt %, more preferably at 20 to 25 wt %, and an inorganic binder at 0 to 90 wt %, preferably at 60 to 90 wt %, more preferably at 75 to 80 wt %. In the embodiments of the above publication, a root canal filling material comprising zirconia beads at 20 wt % is suggested.
However, when using the zirconia beads employed in the above prior art, flowability is low due to the large size of the particles, and water-tightness for preventing bacterial invasion is reduced. Further, sufficient radiopacity cannot be achieved if the content of the zirconia beads is 40 wt % or less as in the above preferable range of the content, thus causing a problem that additional heavy metals are required to be added.
Furthermore, when using 70 to 90% of the inorganic binder in the existing dental filling materials like MTA mainly consisting of calcium silicate cement, calcium hydroxide (CaOH2) produced in the hydration process causes a strong alkaline action to have an irritant effect on dental pulp and paradental tissues for a long time.